1. Field of the Invention
The present invention relates to the field of optically controlled phased array antenna/radar systems. More particularly, the present invention relates to a system for creating continuous true time delays in a photonic beam array system, which is used to produce a microwave beam array with the same time delays to control/steer the propagation direction of the phased array antennas.
2. Description of the Related Art
Phased array antenna systems are well known in the art. A phased array may be used to point a fixed radiation pattern or to scan rapidly in azimuth or elevation.
Such systems can be used, for example, in a tracking system for tracking objects of interest such as aircraft or missiles, and in a high data rate wireless mobile communication system.
In order to steer a microwave beam from a phased array antenna, it is necessary to create a time delay t between the electromagnetic waves generated from each of the neighboring antenna elements in a particular direction.
Traditionally, the time delay in a phased array antenna system has been made by a microwave electronic delay device or an electronic phase shifter (which is not even a true time delay device). However, given the large number of antenna array elements needed, it is necessary to use a large number of delay devices and waveguides (cables), making the overall system very bulky and expensive. Moreover, such systems yield poor quality results.
In the last ten years or so, there have been extensive efforts to develop an optically controlled phased array antenna, in which time delays are generated in the optical domain and then are carried over to the microwave domain using optical fibers. However, most of such proposed schemes have failed because of significant technical difficulties or very expensive material and assembly costs due to their system complexity.
Thus, there exists a need in the art for a simplified and inexpensive system for generating a true time delay in a phased antenna array system.
Accordingly, it is an object of the present invention to provide a simplified and inexpensive true time delay device for optical control of a phased array antenna system.
To this end, according to the present invention, there is provided a true time delay system for optical control of a phased array antenna including a first time delay unit having a pair of parallel end walls having mirrored surfaces facing each other in a zigzag pattern, and an intermediate wall which is substantially parallel to the end walls and has mirrored surfaces on both sides which match the end walls. The intermediate wall also has matching openings in the mirrored surfaces to permit light to pass through the intermediate wall. A displacement unit displaces the intermediate wall relative to the end walls to change the distance that a series of input light beams travels, creating a true time delay in a first dimension. A second time delay unit receives the output of the first time delay unit, provides a time delay in a second dimension and outputs light beams having a time delay in both the first and second dimensions.
More particularly, the present invention is directed to a true time delay generator for optical control of a phased array antenna system having an array of antenna elements arrayed in a first dimension and a second dimension and having a number n of antenna elements in the first dimension and a number m of antenna elements in the second dimension, the generator comprising:
(a) first time delay means for providing a time delay for optical control of the phased array antenna system in the first dimension, the first time delay means for guiding a set of input light beams corresponding to the number n of antenna elements in the first dimension to provide an output comprising a first series of light beams, N in the total number, delayed relative to one another with an equal amount of time delay in the first dimension between each two consecutive light beams of the first series of light beams;
(b) splitter means for splitting each light beam of the first series of light beams to provide an output comprising N groups of M light beams;
(c) second time delay means for providing a time delay for optical control of the phased array antenna in a second dimension, the second time delay means for guiding the output of splitter means to provide an output comprising the N groups of M light beams in which the M light beams in each group are delayed relative to one another to have an equal amount of time delay between each two consecutive light beams in each group in the second dimension, the N groups of light beams constituting signals for optoelectric conversion for steering a propagation direction of the phased array antenna;
wherein the first time delay means comprises a delay generator unit and the second time delay means comprises N delay generator units, each of the delay generator units comprising:
(i) first and second end walls disposed substantially parallel to each other and forming a cavity therebetween, the first end wall having a first plurality of mirrors formed thereon and the second end wall having a second plurality of mirrors formed thereon to face the first plurality of mirrors;
(ii) an intermediate wall disposed between the first and second end walls and being substantially parallel thereto to form a first chamber and a second chamber in the cavity, the intermediate wall having a third and a fourth plurality of mirrors formed on opposite sides thereof to face respectively the first plurality of mirrors of the first end wall and the second plurality of mirrors of the second end wall, the intermediate wall having a series of apertures for passage of the input light beams from the first chamber to the second chamber; and
(iii) displacement means, for example, a motor, for displacing one of (1) the intermediate wall relative to the first and second end walls and (2) the first and second end walls relative to the intermediate wall, so that an area of the first and second chambers is variable for changing a time delay of the optical path of the input light beams in the cavity.
The set of input light beams are input into the first chamber of the first delay means so as to impinge on one of the third mirrors of the intermediate wall of the first delay means and then to reflect between the third mirrors and the first mirrors of the first delay means before passing through the apertures of the first delay means into the second chamber of the first delay means and then to reflect between the fourth mirrors and the second mirrors of the first delay means before passing out of the second chamber of the first time delay means and to the splitter means and then to the N delay generator units of the second time delay means as the N groups of M light beams, and each of the N groups of M light beams are input into the first chamber of a respective one of the N delay generator units so as to impinge on one of the third mirrors of the intermediate wall of the respective one of the N delay generator units and then to reflect between the third mirrors and the first mirrors of the respective one of the N delay generator units before passing through the apertures of the respective one of the N delay generator units into the second chamber of the respective one of the N delay generator units and then to reflect between the fourth mirrors and the second mirrors of the respective one of the N delay generator units before passing out of the second chamber of the respective one of the N delay generator units.
The N delay generator units of the second time delay means may be vertically stacked such that all N first and second end walls are attached together rigidly, and all N intermediate walls are attached together and movable together by the displacement means. The true time delay generator may further comprise amplification means for amplifying the output of the first time delay means. The light source for providing the input light beams may be a light source array positioned at an end of the intermediate wall of the first time delay means and may be a series of collimated lasers. The first, second, third and fourth plurality of mirrors may be curved concavely for retaining a collimation of the input light beams from the light source. A series of collimating lenses may be arranged in optical paths of at least one of the first and second time delay means. The displacement means may displace the intermediate wall relative to the first and second end walls for varying the size of the first and second chambers.
The plurality of mirrors of the intermediate wall and the end walls may be plated with a metal from the group consisting of Au, Ag, Al and Cr. The first and second plurality of mirrors may be arranged in a matching zigzag pattern at approximately xc2x145xc2x0 angles to a normal axis of the first and second walls respectively and having grating surfaces thereon and the third and fourth plurality of mirrors may be arranged in a zigzag pattern at approximately xc2x145xc2x0 angles to a normal axis of the intermediate wall and matching, respectively, the zigzag patterns of the first and second plurality of mirrors. The first and second walls may be connected by a pair of rods and the intermediate wall may be mounted to slide on the pair of rods.
According to another aspect of the present invention, there is provided a true time delay generator, comprising
(a) first and second end walls disposed substantially parallel to each other and forming a cavity therebetween, the first end wall having a first plurality of mirrors formed thereon and the second end wall having a second plurality of mirrors formed thereon to face the first plurality of mirrors;
(b) an intermediate wall disposed between the first and second end walls and being substantially parallel thereto to form a first chamber and a second chamber in the cavity, the intermediate wall having a third and a fourth plurality of mirrors formed on opposite sides thereof to face respectively the first plurality of mirrors of the first end wall and the second plurality of mirrors of the second end wall, the intermediate wall having a series of apertures for passage of the input light beams from the first chamber to the second chamber; and
(c) displacement means for displacing one of (1) the intermediate wall relative to the first and second end walls and (2) the first and second end walls relative to the intermediate wall, so that an area of the first and second chambers is variable for changing a time delay of the optical path of the input light beams in the cavity. Mirrors.
According to yet another aspect of the present invention, there is provided a method of true time delay for optical control of a phased array antenna system having an array of antenna elements arrayed in a first dimension and a second dimension and having a number n of antenna elements in the first dimension and a number m of antenna elements in the second dimension, comprising the steps of:
(a) inputting a set of input light beams, corresponding to the number n of antenna elements in the first dimension, into a first chamber of a first delay unit so as to impinge on one of a plurality of third mirrors of an intermediate wall of the first delay unit;
(b) reflecting the set of input light beams between the third mirrors and a plurality of first mirrors of the first delay unit;
(c) passing the input light beams through a plurality of apertures formed in the first delay unit into a second chamber of the first delay unit;
(d) reflecting the input light beams within the second chamber between fourth mirrors formed on the intermediate wall and second mirrors formed on the second wall of the first delay unit;
(e) passing the input light beams out of the second chamber of the first time delay unit to provide an output comprising a first series of light beams, N in number, delayed relative to one another with an equal amount of time delay in the first dimension between each two consecutive light beams of the first series of light beams;
(f) splitting each light beam of the first series of light beams to provide an output comprising N groups of M light beams;
(g) providing the N groups of M light beams to respectively a first chamber of N delay generator units of a second time delay means so as to impinge on one of a plurality of third mirrors formed on an intermediate wall of the respective ones of the N delay generator units;
(h) reflecting the N groups of M light beams between the third mirrors and first mirrors formed on a first wall of the respective ones of the N delay generator units;
(i) passing the N groups of M light beams through the apertures of the respective ones of the N delay generator units into a second chamber of the respective ones of the N delay generator units;
(j) reflect the N groups of M light beams between fourth mirrors formed on a second wall of the respective ones of the N delay generator units and the second mirrors of the respective ones of the N delay generator units; and
(k) passing the N groups of M light beams out of the second chamber of the respective ones of the N delay generator units.
The method may comprise displacing one of (i) the first and second walls relative to the intermediate wall and (ii) the intermediate wall relative to the first and second end walls, to change a time delay of an optical path of light beams in the first and second chambers. The method may further comprise amplifying the output of the first time delay unit; and splitting the output amplified in step (v) for input to the plurality of N generator units of the second time delay unit. The method may further comprise collimating the series of input beams provided to the first delay unit.